The present invention relates to a portable data collection device including an imaging based dataform reader and, more particularly, to a portable data collection device including an imaging based dataform reader utilizing a piezoelectric reflector for optimizing the focal length of the dataform reader.
Portable data collection devices are widely used in manufacturing, service and package delivery industries to perform a variety of on-site data collection activities. Such portable data collection devices often include integrated bar code dataform readers adapted to read bar code dataforms affixed to products, product packaging and/or containers in warehouses, retail stores, shipping terminals, for inventory control, tracking, production control and expediting, quality assurance and other purposes.
Bar code dataforms come in a variety of different formats including one and two dimensional bar codes, matrix codes and graphic codes, as well as words and numbers and other symbols, which may be printed or etched on paper, plastic cards and metallic and other items. For example, a one dimensional bar code dataform typically consists of a series of parallel light and dark rectangular areas of varying widths. The light areas are often referred to as xe2x80x9cspacesxe2x80x9d and the dark areas as xe2x80x9cbarsxe2x80x9d. Different widths of bars and spaces define different characters in a particular bar code dataform.
Data originally encoded in a dataform is recovered for further use in a variety of ways. For example, a printed bar code may be illuminated to derive reflectance values which are digitized, stored in buffer memory and subsequently decoded to recover the data encoded in the bar code. The printed bar code may be illuminated using a laser, an array of LEDs, ambient light, or the like. The light reflected from the printed bar code typically is captured using a photosensor such as, for example, a CCD detector or CMOS detector.
A problem associated with conventional dataform readers is that the readers are designed to read dataforms located within a limited range therefrom. For example, a dataform reader may be designed to read dataforms located within the range of three inches to twelve inches from the reader. The maximum distance at which a dataform reader is able to read a dataform is limited by a resolution of the photodetector used to capture the dataform. For example, using a conventional 640 horizontal pixel photosensor, one dimensional bar code dataforms can be read so long as the distance the reader is placed from the dataform is such that the 640 horizontal pixels are suitable to distinguish among the narrowest bars and spaces forming the dataform. As the dataform reader is moved further away from a dataform, the images of the bars and spaces appear smaller at the photosensor thereby limiting the range at which the dataform reader is able to read a dataform.
One way to allow the dataform reader to read the dataform at longer distances or at different focal lengths is to increase the resolution of the photosensor. For example, rather than providing 640 horizontal pixels, the photosensor may include 1000 or more horizontal pixels. In this manner, the photosensor is able to distinguish among smaller features of the dataform thereby enabling reading of dataforms located farther away. A significant drawback to increasing the number of horizontal pixels on the photosensor is that a width of the photosensor becomes proportionately larger in order to accommodate the additional pixels. As the width of the photosensor increases, so does the overall width of the reader module. Unfortunately, due to customer demand for smaller and more compact dataform readers, the ability to increase the width of the reader module is often not a feasible option.
A method employed to provide different focal lengths for the same dataform reader is to utilize several mirrors and lenses at varying distances within the dataform reader for focusing the image on different photosensor arrays. This complicates the construction of the device and increases the cost since lens assemblies for these particular devices are quite expensive. In addition, the logic circuitry within the dataform reader must choose between the best focus amongst the different photosensor arrays, which is not necessarily the optimal focus. Many times, motors and other electromechanical devices are employed to move the mirrors and/or lenses. Unfortunately, mechanical components such as motors and moving mirrors tend to wear over time which may ultimately produce mechanical failures in the scanners.
Other techniques have evolved which employ electronic systems to choose an optimal focal length for a particular reading. While solving some of the aforementioned problems with moving mechanical components, many of these electronic systems are fabricated by employing elaborate processes and materials. Also, many conventional electronic systems employ complicated geometrical shapes and structures to achieve desired scanning results.
Accordingly, there is a strong need in the art for a dataform reader which is capable of reading dataforms at varying distances which overcomes the aforementioned drawbacks.
The present invention provides for a dataform reader utilizing a piezoelectric reflector with a reflection angle that is adjustable to provide for an optimal focus of an image projected onto a photosensor array. A distance measurement device can provide a distance measurement utilized in adjusting the piezoelectric reflector, such that an optimal focus can be made without the use of multiple lenses and/or reflectors. Alternatively, various dataform readings can be performed to find the optimal focus without employing a distance measurement device. Additionally, distance measurements and readings can be performed on segments of the dataform and the dataform reconstructed after all of the readings have been performed. This provides for maximizing the pixel data captured by the photosensor array, while also enabling the dataform reader to perform readings on dataforms that do not lie within a single plane, for example, round dataforms. Furthermore, the dataform reader can perform readings when the dataform reader is inclined relative to the dataform.
According to one aspect of the invention, a dataform reading module is provided. The dataform reading module includes a photosensor, a lens for focusing a respective image representing a dataform taken along a target line onto the photosensor and a piezoelectric reflector configured to direct an image of the dataform taken along the target line onto the lens. The piezoelectric reflected is adjustable based on an optimal focus measurement. The dataform reading module also includes an illuminating device for illuminating the dataform.
According to another aspect of the invention, a dataform reader for reading a dataform is provided. The dataform reader includes a hand-portable sized housing having at least one lens and a reading module included within the housing. The reading module includes a photosensor array and a piezoelectric reflector for directing a respective image representing the dataform along a target line onto the at least one lens. The piezoelectric reflector is adjustable based on an optimal focus measurement. The at least one lens and the piezoelectric reflector are configured to focus an image of the dataform along the target line onto the photosensor array. The dataform reader also includes an illuminating device for illuminating the dataform.
According to yet another aspect of the invention, a method for reading a dataform employing a dataform reading module is provided. The method includes the steps of making an optimal focus measurement based on a focal length of the dataform reading module from the dataform, adjusting an angle of reflection of a piezoelectric reflector based on the optimal focus measurement, focusing an image of the dataform taken along a target line reflected from the piezoelectric reflector through a lens assembly onto a photosensor array and reconstructing a final image of the dataform taken along the target line.
According to still yet another aspect of the invention, a dataform reading module is provided. The dataform reading module including means for reflecting a dataform to a means for capturing images of a dataform, means for adjusting the reflection angle of the means for reflecting a dataform to provide an adjustable focus length of the dataform reading module, the means for adjusting the reflection angle being based on an optimal focus measurement and means for reconstructing the image of the dataform.
These and other aspects, features and advantages of the invention will become better understood from the detailed description of the preferred embodiments of the invention which are described in conjunction with the accompanying drawings.